1. Field of the Invention
The present invention relates in general to a image obtaining method and apparatus for an endoscope apparatus, and in particular to an image obtaining method and apparatus for an endoscope apparatus wherein a low-intensity fluorescent light image and a high-intensity standard image are received by use of the same photoelectrical converting element.
2. Description of the Related Art
Endoscope apparatuses for observing living tissues within a body cavity are widely known, and there are in wide use today electronic endoscope apparatuses wherein an illuminating light such as a white light or the like for observing living tissue is projected into a subject body cavity and an image of the living tissue illuminated thereby is obtained by use of a CCD element or the like, and this image is observed on a television screen. Further, the living tissue within the body cavity is not only illuminated by an illuminating light such as a white light or the like and observed: endoscope apparatuses that obtain a visible image formed based on a standardized fluorescent light intensity, which represents the ratio between the intensity of the fluorescent light near the wavelength range of 480 nm and the intensity of the fluorescent light in the wavelength range spanning from 430-730 nm emitted from the living tissue within the body cavity upon the irradiation thereof by an excitation light of a wavelength near 410 nm; or a visible image based on a fluorescent light yield ratio, which represents the ratio between the intensity of the fluorescent light emitted from the living tissue within the body cavity upon the irradiation thereof by the aforementioned excitation light and the intensity of the near infrared light reflected from the aforementioned living tissue upon the irradiation thereof by a near infrared light, which is a reference light, for use in diagnosing the tissue state of a target tissue have also been proposed. Note that the excitation light is readily absorbed by the living tissue, and because it is difficult to use the excitation light intensity received by the target tissue for measurement, near infrared light or a red light or the like, which is not readily absorbed by the living tissue, is employed as a reference light, and the excitation light intensity received by the living tissue is measured.
Because there is a large difference between the light intensity of a standard image formed of the high-intensity illuminating light that has been reflected from a living tissue that has been irradiated thereby and a fluorescent image formed of the low-intensity fluorescent light emitted from a living tissue upon the irradiation thereof by an excitation light, if, for example, these two images were to be time divided and obtained by the same image obtaining element, a dynamic range on the order of 90 dB (approximately 65000 gradations) would be required. However, the dynamic range of a currently available typical photoelectrical converting element is 60 dB (approximately 1000 gradations); therefore, an operation wherein, for example, a standard image only is passed through a light reducing filter and the light passing therethrough is received; and the standard image and the fluorescent image are both within a dynamic range below 60 dB and the light thereof is received; wherein the standard image and the fluorescent image received thereby are each photoelectrically converted and obtained as an analog signal, respectively, is performed. Then, these analog signals are converted to digital values after being amplified by a roughly fixed predetermined gain, and these digital values are used to form a visible image of the aforementioned living tissue and said visible image is observed, or the fluorescent light yield, the standardized fluorescent light intensity or the like is obtained and a visible image representing the tissue state of the aforementioned living tissue is formed and a diagnosis is carried out.
On the other hand, research and development of photoelectrical converting elements having a dynamic range of 90 db is also progressing, and if a photoelectric converting element having a dynamic range enlarged to this extent is employed, the standard image and the fluorescent image can be received by the same photoelectric converting element within the dynamic range thereof without the standard image having to first be passed through a light reducing filter or the like, and the light intensity of the standard image received by the photoelectric converting element becomes higher. In this manner, the ratio of photon noise generated in proportion to the square root of the received light intensity can be largely reduced, and because the S/N ratio of the standard image can be improved, it is desirable that a photoelectric converting element having an enlarged dynamic range such as this be utilized in an endoscope apparatus.
However, the analog signal obtained by a photoelectric converting element having a wide dynamic range such as this has a wide dynamic range, and the circuitry for processing said wide dynamic range analog signal, such as an A/D converting circuit, a computational circuit or the like, must also have the same wide dynamic range (such as 90 dB or 16 bits), and there is a problem in that it is difficult to construct such circuitry. That is to say, a circuit having a wide dynamic range such as this and the elements configuring said circuit are not common; they are extremely expensive; particularly in the case of disposing a photoelectric converting element having a wide dynamic range (e.g., 90 dB) in the distal end of an endoscope apparatus, in which signals are transmitted through a narrow tube, there is the fear of a problem due to noise becoming mixed in with the signal during transmission.
The present invention has been developed in consideration of the circumstances described above, and it is a primary objective of the present invention to provide an image obtaining method and apparatus for an endoscope apparatus, which are capable of converting a photoelectrically converted and outputted analog signal to a digital value having a narrower dynamic range, while suppressing the reduction of the gradations of said analog signal, whereby the mixing of noise with said digital value can be suppressed, and the cost of the apparatus can be reduced.
The image obtaining method of the endoscope apparatus according to the present invention comprises the steps of: irradiating a living tissue with an illuminating light and an excitation light, each of which is emitted at a mutually different timing; receiving, by use of the same photoelectric converting element, a fluorescent image formed of the fluorescent light emitted from the living tissue upon the irradiation thereof by the excitation light and a standard image formed of the reflected light reflected from the living tissue upon the irradiation thereof by the illuminating light; photoelectrically converting the standard image and the fluorescent image received thereby, to obtain each as respective analog signals; converting these analog signals to respective digital values; and outputting these digital values as an image signal; wherein, the analog signal representing the fluorescent image is converted to digital values after being amplified by a larger gain than the gain utilized in amplifying the analog signal representing the standard image.
The image obtaining apparatus of the endoscope apparatus according to the present invention comprises: an illuminating means for irradiating a living tissue with an illuminating light and an excitation light, each of which is emitted at a mutually different timing; a light receiving means for receiving a fluorescent image formed of the fluorescent light emitted from the living tissue upon the irradiation thereof by the excitation light, and a standard image formed of the reflected light reflected from the living tissue upon the irradiation thereof by the illuminating light, and photoelectrically converting the standard image and the fluorescent image received thereby to respective analog signals and outputting said analog signals; an amplifying means for amplifying said analog signals; and an A/D converting means for converting the amplified analog signals to respective digital values; wherein, the amplifying means amplifies the analog signal representing the fluorescent image by a larger gain than that utilized in amplifying the analog signal representing the standard image.
It is preferable that the gain of the amplifying means be set so that the largest value of the analog signal representing the fluorescent image becomes substantially equivalent to the largest value of the analog signal representing the standard image.
The amplifying means comprises a floating diffusion amplifier for converting to voltages the analog signal representing the fluorescent image outputted from the light receiving means, and an A/D conversion gain adjusting amplifier for amplifying the output voltage from said floating diffusion amplifier; wherein the gain thereof can be the gain of the floating diffusion amplifier and/or the A/D conversion gain adjusting amplifier. Here, the referent of the xe2x80x9candxe2x80x9d of the expression xe2x80x9cthe gain can be the gain of the floating diffusion amplifier and/or the A/D conversion gain adjusting amplifierxe2x80x9d is that the gain of the amplifying means can be the gain of the floating diffusion amplifier multiplied by the gain of the A/D conversion gain adjusting amplifier.
The gain is set based on respective histograms representing the distribution of the light intensity of the fluorescent image and the standard image, which have been formed using digital values; so that the largest value of each of the respective histograms can be substantially equal.
The gain can be selected from among a plurality of preset stepped values.
As to the technique for amplifying the analog signal representing the fluorescent image by a larger gain than that utilized to amplify the analog signal representing the standard image, a method such as that described below can be employed.
That is to say, a method wherein: the gain used when amplifying the analog signal representing the fluorescent image (hereinafter referred to as the fluorescent image gain) and the gain used when amplifying the analog signal representing the standard image (hereinafter referred to as the standard image gain) are set so that the fluorescent image gain is larger than the standard image gain; the fluorescent image gain is employed when the analog signal representing the fluorescent image is to be amplified; and the standard image gain is employed when the analog signal representing the standard image is to be amplified, can be employed. This means differs from a means such as an automatic gain controller (AGC), which automatically adjusts the amplification gain of the analog signal representing a photoelectrically converted image converted after the input of the image data representing the image before the photoelectrical conversion thereof, based on the input image data.
Further, according to the image obtaining method and apparatus for an endoscope apparatus of the present invention, an A/D converting means for converting the analog signal representing the fluorescent image to digital values having a smaller input range than that of the analog signal representing the standard image, can be provided instead of the means for amplifying the analog signal representing the fluorescent image by a larger gain than that utilized to amplify the analog signal representing the standard image.
It is preferable that this A/D converter be provided so as to be capable of switching the input range so that the largest value of the digital values representing the fluorescent image becomes substantially equal to the largest value of the digital values representing the standard image.
The input range can be set based on respective histograms representing the distribution of the light intensity of the fluorescent image and the standard image, which have been formed using digital values; so that the largest value of each of the respective histograms can be substantially equal.
The input range can be selected from among a plurality of preset stepped values.
The fluorescent image can be a fluorescent image formed of a plurality of mutually different wavelength ranges of fluorescent light, into each of which fluorescent light has been divided spectrally in a time division manner.
The illuminating light can be light containing wavelengths within the near infrared wavelength range.
It is preferable that the A/D converter be a means for converting the analog signal outputted from the amplifying means to a digital value containing 14 bits or less of data.
It is preferable that the light receiving means be a charge multiplying photoelectric converting element.
Note that the input range refers to the input range (full-scale input range) of the maximum analog signal value capable of being A/D converted by the A/D converter.
According to the photographing method and apparatus of the endoscope apparatus of the present invention: in outputting an image signal formed of the digital values, which the respective analog signals representing a fluorescent image and a standard image that have been received and photoelectrically converted at the same photoelectric converting element, have been converted to, because the analog signal representing the fluorescent image (hereinafter referred to as the fluorescent image analog signal), which has been received at a low intensity is formed of small signal values, is amplified by a gain larger than that used for amplifying the analog signal representing the standard image (hereinafter referred to as the standard image analog signal), which has been received at a high-intensity and is formed of large signal values, and then converted to digital values, the fluorescent image analog signal can be correlated to a higher order digital values region and converted; compared to cases in which the fluorescent image analog signal and the standard image analog signal have been amplified by the same gain, the fluorescent image analog signal can be converted to digital values wherein the losses in the gradations of the image data borne by the fluorescent image analog signal can be suppressed. That is to say, the fluorescent image analog signal can be represented as digital values divided into quantization units of a smaller signal level than those of the standard image analog signal.
Further, for cases in which the dynamic range of the digital values has been set so as to be of a narrower dynamic range than the dynamic range of the values of the analog signals, the fluorescent image analog signal can be converted to digital values of a narrow dynamic range wherein the reduction of the gradations can be suppressed, and the circuitry for processing these digital signals can be simpler than that used for processing the signals having a dynamic range similar to those of the analog signals; because the circuitry for processing these digital values can be configured so as to have a narrower dynamic range, the cost of the apparatus can be reduced, and an effect whereby the noise becoming mixed with the signal within such circuitry having a narrow dynamic range is suppressed can be expected.
Note that although there is a loss of gradations in the standard image represented by the standard image analog signal when said analog signal is converted to digital values, because the standard image analog signal has higher gradations formed of larger signal values than those of the fluorescent image analog signal, even if the gradations of the image data borne by the standard image analog signal undergo reduction somewhat, there will be little reduction of the quality of the image data thereof; further, there will also be almost no adverse effect on the accuracy of the computations performed to obtain the fluorescent light yield and the like.
Here, if the amplifying means is a means that sets the gain thereof so that the largest value of the fluorescent analog signal becomes substantially equal to the largest value of the standard image analog signal, because the fluorescent image analog signal, which is formed of smaller signal values than those of the standard image analog signal, can be amplified to a size equivalent to that of the standard image analog signal and then converted to digital values, the fluorescent image analog signal can be converted to digital values in a manner that ensures the suppression of the reduction of the gradations in the image data borne by said fluorescent image analog signal.
Further, if the amplifying means is provided with a floating diffusion amplifier for converting to voltages the analog signals outputted from the light receiving means, and an A/D conversion gain adjusting amplifier for amplifying the output voltage of said floating diffusion amplifier, and the gain is made to be the gain of the floating diffusion amplifier and/or the A/D conversion gain adjusting amplifier, the fluorescent image analog signal can be more easily amplified by a gain larger than that by which the standard image fluorescent image analog signal is amplified.
Note that if the gain is set, based on the respective histograms representing the light intensity distributions of the fluorescent image and the standard image and which have been formed utilizing digital values, so that the largest value of the light intensity represented by each histogram is substantially equal, the reduction of the gradations of the fluorescent image occurring when the digitization thereof is performed can be positively suppressed to be less. Further, if the gain is selected from among a plurality of preset stepped values, changing the gain can be performed by a simpler circuitry.
Further, according to another photographing method and apparatus for an endoscope apparatus of the present invention, an A/D converter has been provided which converts the fluorescent image analog signal to a digital value with a narrower input range than that for the standard image analog signal, instead of the amplifying means that amplifies the fluorescent image analog signal with a larger gain than that for the standard image analog signal. Thereby, the fluorescent image analog signal can be converted to digital values corresponding to a range of a higher order. Compared to the case in which the fluorescent image analog signal and the standard image analog signal are converted at the same input range, the fluorescent image analog signal can be converted to digital values while suppressing the loss of gradations in the image data borne thereby. That is, the fluorescent image analog signal can be expressed as a digital value which has been divided into signal levels having a lower quantization unit than that of the standard image analog signal.
Note that in the case that the dynamic range of the digital values is set to be narrower than the dynamic range of the analog signals, the fluorescent image analog signals can be converted to digital values having a narrower dynamic range while suppressing the reduction in gradation thereof. Therefore, the circuitry to process these digital values can be constructed of simpler circuits having a narrower dynamic range than that of the circuits having the dynamic range of the analog signals, whereby the cost of the apparatus can be reduced. Further, an effect can be expected that the noise mixed in with the signals will be reduced by the use of a circuit structure having a narrow dynamic range.
Further, if the A/D converter be provided so as to be capable of switching the input range so that the largest value of the digital values representing the fluorescent image becomes substantially equal to the largest value of the digital values representing the standard image, because the fluorescent image analog signal, which is formed of signal values smaller than those of the standard image analog signal, can be converted to digital values of the same size as those of the standard image signal, said fluorescent image analog signal can be converted to digital values wherein the reductions occurring in the gradations of the image data represented by said fluorescent image analog signal can be more positively suppressed.
Still further, if the input ranges are set based on the respective histograms, which have been formed using digital values and which represent the respective distributions of the light intensity of the fluorescent image and the standard image, so that the largest value of the light intensity distribution occurring within each said histogram become substantially equal, the reduction of the gradations occurring in the fluorescent image when the digitization thereof is performed can be positively suppressed to be less; further, if this input range is selected from among a plurality of preset stepped values, changing said input range can be performed more simply.
Note that if the fluorescent image is an image formed of a plurality of mutually different wavelength ranges of fluorescent light, into each of which fluorescent light has been divided spectrally in a time division manner, and the standard image is an image containing wavelengths of light within the near infrared wavelength range, the application thereof in fluorescent image diagnosis becomes easier.
Further, if the A/D converter is a means for converting the analog signal outputted from the amplifying means to a digital value containing 14 bits of data or less, the circuitry down line from the A/D converter can be easily configured.
Still further, if the light receiving means is a charge multiplying photoelectric converting element, the standard image can be obtained as a standard image analog signal having a higher S/N ratio.